The present study is an analysis of the relationship of single neuronal activity in the midbrain periaqueductal gray (PAG) of the monkey to muscles of the laryngeal and respiratory systems during vocalization. Prior work has shown the PAG to be important in vocalization, and the activity of PAG neurons either facilitates or suppresses the activity of some laryngeal muscles. The present study will address more specifically which laryngeal and respiratory muscles are influenced by the PAG as well as how different sets of PAG neurons behave during vocalization. Macaca nemestrina monkeys will be trained to vocalize, and then under general anesthesia and using aseptic techniques, electrodes will be implanted in the brain and muscles of the laryngeal and respiratory systems. After recovery from surgery, single PAG neurons will be extracellularly recorded while the monkeys are vocalizing. The nucleus ambiguus (NA), the site of laryngeal MNs and neurons related to respiratory activity, will be stimulated through a chronicallly implanted electrode to antidromically activate PAG neurons. Electromyographic (EMG) electrodes will be used to record the activitiy of the laryngeal and respiratory muscles. PAG unit activity will also be related to EMG activity in the different muscles. The combined approach of PAG extracellular recording, NA stimulation and EMG recording will help to determine how activity of single PAG neurons are involved in the control of various synergistic and antagonistic muscles of the vocalization system. This study will help us to learn how the brain controls vocalization in primates. This knowledge will aid in understanding the neural control of vocalization in humans and in understanding the mechanisms by which various neurological diseases manifest themselves in human vocalization and speech.